The present invention relates to a semiconductor device and a method for manufacturing a semiconductor device, and more specifically, to a technology of forming transistors having a stacked structure in a peripheral circuit region and forming a NMOS transistor of an upper layer over a silicon germanium layer and a silicon layer to have a tensile strain structure, thereby increasing electron mobility of a channel region in operation of the device.
Due to high integration of semiconductor devices, an area occupied by a device has been reduced. As a result, a transistor size becomes smaller, a space between a source region and a drain region becomes narrower, and a channel length becomes shorter. Also, a size of a contact plug that contacts with the source/drain region of the transistor is reduced.
When the size of the contact plug is reduced, a contact resistance (Rc) between a silicon substrate and the contact plug is increased. As a result, a current characteristic of the device is degraded obstructing high speed operation of the device.